300 Solar System

The solar system consists of planets and other bodies that orbit the sun in predictable paths. As the basis for understanding this concept, students know:

the sun, an average star, is the central and largest body in the solar system and is composed primarily of hydrogen and helium.

the solar system includes the Earth, moon, sun, eight other planets and their satellites, and smaller objects such as asteroids and comets.

the path of a planet around the sun is due to the gravitational attraction between the sun and the planet.

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II. Goals of this module -

To learn about the various components of the solar system.

To learn how and why the movement patterns of the sun, moon, and planets vary with respect to the constant background of the stars.

To learn the definitions of and proper spelling for scientific terms that are used commonly in newspapers, magazines, and books, and on television and radio programs to discuss or explain the solar system.

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III. Origin of the solar system -

Formed from a rotating nebula.

Began to contract due to gravitational attraction of particles in the nebula.

Contraction produced high temperatures, faster rotation, and flattening into a disk; all elements were in gaseous form due to extremely high temperatures.

As temperature decreased, the central portion of the nebula eventually formed the Sun, while outer concentrations of gas at cooler temperatures produced liquid and solid substances that contracted and became planets and moons.

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IV. Interior structure of the Sun -

Core - 50% of the diameter; fusion takes place here in a plasma.

Radiative zone - extends to 70% of the diameter; gamma rays converted to X rays and ultraviolet rays here.

Convective zone - remaining 30% of the diameter; gases here are very turbulent.

Photosphere - the visible surface of the sun; electromagnetic radiation converted to visible light here; 6,000°K.

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V. Sunspots -

Occur on the photosphere.

Relatively cool areas; only 4,000°K.

Their movement indicates that the Sun is rotating.

Alternately increase and decrease in number on an 11-year cycle.

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VI. Atmosphere of the Sun -

Chromosphere - contains solar flares and prominences.

Corona - extremely low-density plasma; temperature of 2,000,000°K.

The chromosphere and the corona are seen only during eclipses of the Sun.

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VII. Planet groups -

Inner (terrestrial) planets -

Mercury, Venus, Earth, and Mars (in order from closest to sun).

Commonly are hot and small, have weak gravity and little gaseous atmosphere because any original gases easily reached escape velocity (the velocity required in order for one object to escape from either crashing into or continuously orbiting another object).

Outer (Jovian) planets -

Jupiter, Saturn, Uranus, and Neptune (in order from closest to sun).

Commonly are cold and large, have strong gravity and lots of gaseous atmosphere because the gases could not reach escape velocity; also have extreme winds, and many frozen substances.

Pluto -

Discovered in 1930 as a result of mathematical calculations. The true nature of this planet is a mystery.

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VIII. Motions of astronomical objects -

Rotation - spinning of an object on its axis (an imaginary line between the poles about which the object rotates).

Revolution - movement of an object in its orbit (the path of one object around another) around another object.

Inclination of the axis - the number of degrees that the rotational axis of an object is inclined from a line that is perpendicular to the plane of its orbit around another object.

Phases of Mercury and Venus -

These two planets have phases like the Earth's Moon because they revolve inside the orbit of the Earth and are sometimes between the Sun and the Earth and sometimes behind the Sun.

Apparent motion of Mercury and Venus -

Seen only as morning and evening "stars" because they revolve inside the orbit of the Earth.

Retrograde motion of planets beyond the Earth -

The apparent backward motion of the planets as the Earth passes by them on its closer and interior orbit.

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IX. Planetary highlights -

Mercury - MORE ABOUT MERCURY About the size of the Earth's moon. All atmosphere has escaped, so there are many craters. Has the second slowest rotation rate of all the planets = 59 days; hence the days will be long and hot; and the nights, long and cold. Revolution occurs in 88 days.
Venus - MORE ABOUT VENUS About the same size as the Earth. Thick atmospheric cloud cover; 96% carbon dioxide. Has the slowest rotation rate of all the planets = 243 days.
Earth - MORE ABOUT EARTH Average distance from the Sun is ~150,000,000 km (~93,000,000 mi). Diameter equals ~12,800 km (~8,000 mi). Sidereal rotation period (rotation with respect to the stars) is 23 hrs and 56 min; rotation period with respect to the Sun is 24 hrs or 1 solar day. Period of revolution is 365.26 solar days. Inclination of its axis is ~23.5°. Known as the water planet because of its vast oceans.
Mars - MORE ABOUT MARS Has a very thin atmosphere; 95% carbon dioxide. Has frozen carbon dioxide (dry ice) polar caps.
Jupiter - MORE ABOUT JUPITER The largest planet; about 11 times the diameter of the Earth. Has the fastest rotation speed; 9 hours and 50 minutes. Has a giant red spot in its atmosphere; a cyclonic storm that rotates once every 12 days. Four of Jupiter's moons are large enough to be seen with binoculars.
Saturn - MORE ABOUT SATURN The planet with the most visible rings. Has more moons (23) than any other planet.
Uranus - MORE ABOUT URANUS The sideways planet; the inclination of its axis is 98° hence it rotates in a direction opposite to the other planets.
Neptune - MORE ABOUT NEPTUNE Distance from the Sun is ~4,500,000,000 km (~2,800,000,000 mi). A very windy planet; up to 600 miles per hour winds. Its largest moon, Triton, revolves in the opposite direction of the other moons.
Pluto - MORE ABOUT PLUTO Revolution takes 248 years. Has a very elliptical orbit; sometimes coming closer to us than Neptune. Once was perhaps a moon of Neptune that was displaced by collision with a large meteoroid.

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X. Asteroids and Comets -

Asteroids - microplanets

Most occur in orbits between Mars and Jupiter.

Comets -

Bodies of frozen gases.

Very elliptical orbits around the sun.

When inside the orbit of Saturn, the frozen gases vaporize and become visible.

Most are about the size of Jupiter.

The tail always points away from the Sun because it is being pushed away from the Sun by the solar wind.

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XI. Earth's Moon -

Average distance from the Earth is ~382,000 km (~237,000 mi); equal to about 9 1/2 trips around the Earth.

Diameter equals ~3,500 km (~2,200 mi); about 1/4 the diameter of the Earth.

Sidereal revolution period is 27 1/3 solar days (= 1 sidereal month); revolution period with respect to the Sun is 29 1/2 solar days (= 1 synodic month).

Rotation period equals one synodic month, so the same side of the Moon is always facing the Earth.

All atmosphere has escaped, so there are many craters.

Phases of the Moon - the portion of the Moon that we see from the Earth that is illuminated by the Sun changes in a cyclic pattern with a period of one synodic month. Click here to see different phases of the moon for the last 200 years and the next 200 years.

New Moon - no Moon seen; illuminated side faces away from the Earth.

Waxing crescent Moon - the illuminated portion of the Moon seen from the Earth is crescent shaped and the amount seen increases in size nightly; seen mostly during daylight hours to the east of the sun.

First quarter Moon - exactly half of the illuminated portion of Moon is visible; seen in the eastern sky between noon and sunset, directly overhead at sunset, and in the western sky between sunset and midnight.

Waxing gibbous Moon - more than half of the illuminated portion of the Moon is seen from the Earth and the amount increases nightly; seen in the afternoon hours before and after sunset.

Full Moon - all of the illuminated portion of the Moon is visible; seen in the eastern sky between sunset and midnight, directly overhead at midnight, and in the western sky between midnight and sunrise.

Waning gibbous Moon - more than half of the illuminated portion of the Moon is seen from the Earth and the amount decreases nightly; seen in the morning hours before and after sunrise.

Third quarter Moon - exactly half of the illuminated portion of Moon is visible; seen in the eastern sky between midnight and sunrise, directly overhead at sunrise, and in the western sky between sunrise and noon.

Waning crescent Moon - the illuminated portion of the Moon seen from the Earth is crescent shaped and the amount seen decreases in size nightly; seen mostly during daylight hours to the west of the sun.

Eclipses -

Lunar - moon goes into the Earth's shadow.

Solar - moon goes in front of the sun.

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XII. Meteoroids -

Space particles captured by Earth's gravity.

They burn up as they pass through Earth's atmosphere; thus making a streak of light.

Meteorites are meteoroids that have survived passage through Earth's atmosphere, have crashed into the Earth, and have been found.

Craters are created by meteorite impact.

XIII. Laboratory exercises -

EXAMINE THE ORIGIN OF THE PHASES OF THE MOON -

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XIV. Possible essay questions -

Describe the origin of the solar system.

Describe the Sun and all of its various parts.

List all of the planets of the solar system in order from closest to farthest from the Sun, and state an important characteristic for each one.

Describe and illustrate why it is that Mercury and Venus have phases like the moon.

Describe and illustrate why Mercury and Venus appear only as morning and evening "stars".

Describe two important characteristics of both asteroids and comets.

Describe and illustrate the eight major phases of the moon and illustrate the relative positions of the Sun, Earth, and Moon for each of the phases.

Describe and illustrate the relative positions of the Earth, Sun, and Moon during lunar and solar eclipses.

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XV. Practice Questions

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